Optical short-time variability properties of AGN Ester Aranzana E. Körding, P. Uttley, S. Scaringi X-ray Universe 6-9 June 2017, Rome
AGN variability Characteristic time-scales (different physical mechanisms) Light crossing time-scale ~ hours Dynamical time-scale ~ days Thermal time-scale ~ years Viscous time-scale ~ tens of years McHardy (2009)
AGN variability Characteristic time-scales (different physical mechanisms) Light crossing time-scale ~ hours Dynamical time-scale ~ days Thermal time-scale ~ years Viscous time-scale ~ tens of years t b M 2.17 BH L 0.90 bol McHardy (2009)
AGN variability Characteristic time-scales (different physical mechanisms) Light crossing time-scale ~ hours Dynamical time-scale ~ days Thermal time-scale ~ years Viscous time-scale ~ tens of years Amplitude of variability t b M 2.17 BH L 0.90 bol (%) = s Z 2 1 P( )d McHardy (2009)
Why studying optical variability of AGN? Long-term variability: SDSS, Palomar Green Quasars, PanSTARRS Short-term variability: handful of selected sources with Kepler Simm et al. 2015 Mushotzy et al. 2011
Why studying optical variability of AGN? Origin of rapid optical variability? Jet Reprocessing of X-rays Disc instabilities Is there a cosmological evolution on the variability properties of the AGN? Accretion states? Variability properties associated to a certain BH mass or luminosity? Ester Aranzana Ester Aranzana The optical rms-flux relation: Optical from variability CVs to properties AGNs of AGN X-ray Universe 6-9 June NAC 2017, 21st Rome of May 2015
Sample selection and observations with K2 275 AGN selected from the Million Quasar Catalogue with R > 19 (Flesch 2013) Duration: 80 days Cadence: 29.4 min Bandpass: 420-900 nm Ester Aranzana Optical variability properties of AGN X-ray Universe 6-9 June 2017, Rome
Monte Carlo simulations of power spectra Uttley et al. 2002
Monte Carlo simulations of power spectra Uttley et al. 2002
Monte Carlo simulations of power spectra Lomb-Scargle Pobs Uttley et al. 2002
Monte Carlo simulations of power spectra Lomb-Scargle Pobs P =A 0 Count rate Time Uttley et al. 2002
Monte Carlo simulations of power spectra Lomb-Scargle Pobs P =A 0 Psim Count rate Time Uttley et al. 2002
Monte Carlo simulations of power spectra Lomb-Scargle Pobs P =A 0 Psim Count rate 2 dist = NX i=1 (P sim P obs ) 2 ( P sim ) 2 Time Uttley et al. 2002
Power-law model Aranzana et al. 2017 (submitted)
Power-law model Observed Simulated Aranzana et al. 2017 (submitted)
Power-law model Observed Simulated PL model works! Aranzana et al. 2017 (submitted)
Results Steep PL -2.5, steeper than X-ray PSDs Aranzana et al. 2017 (submitted)
Results Steep PL -2.5, steeper than X-ray PSDs The amplitude of variability is 2.6 % Aranzana et al. 2017 (submitted)
Results Steep PL -2.5, steeper than X-ray PSDs The amplitude of variability is 2.6 % Aranzana et al. 2017 (submitted)
Cosmological evolution of AGN? It is attributed to a wavelength dependence of the variability Aranzana et al. 2017 (submitted)
Summary First AGN catalogue with K2 PSDs of Kepler AGN are well described by a PL model PSDs steeper than the PSDs in X-rays Correlation amplitude of variability and redshift associated to wavelength dependence No anti-correlation found between the variability and the bolometric luminosity Short-time optical variability studies are excellent to identify blazars and confirm AGN candidates Follow-up: Correlations with black hole mass, radio loudness
Difference with X-ray PSDs Associated to two effects: Viscous damping of high-frequency fluctuations Filtering effect of the extended region observed with Kepler see Arevalo & Uttley 2006
Anti-correlation with bolometric luminosity? Simm et al. 2015 Aranzana et al. 2017 (submitted)
Anti-correlation with bolometric luminosity? Hours Simm et al. 2015 Aranzana et al. 2017 (submitted)
Anti-correlation with bolometric luminosity? Hours Simm et al. 2015 Aranzana et al. 2017 (submitted)